Diversity and origin of rheumatologic autoantibodies

Chemokine CXCL1 as a potential marker of disease activity in systemic lupus erythematosus

Objectives

The chemokine CXCL1, known as growth-related oncogene α (GRO-α), is a potent chemoattractant and regulator of neutrophils. The purpose of our study was to evaluate the regulatory response of CXCL1 in the serum of patients with systemic lupus erythematosus (SLE) in the active stage of disease and to assess whether it was implicated in the pathogenesis/inflammatory process in lupus.

Methods

CXCL1 serum concentrations were examined in 90 SLE patients, 56 other autoimmune diseases (OADs) patients and 100 healthy controls using enzyme-linked immunosorbent methodology.

Results

SLE patients exhibited significant increases in serum CXCL1 concentrations [1492.86 (735.47–2887.34) pg/ml] compared with OADs patients [155.88 (10.77–366.78) pg/ml] and healthy controls [13.58 (8.46–37.22) pg/ml] (p < 0.001). Moreover, the level of CXCL1 decreased as the level of anti-dsDNA IgG decreased after treatment between the anti-dsDNA-positive SLE patients and the anti-dsDNA-negative SLE patients. Additionly, serum CXCL1 concentrations were related to different disease activity levels in SLE and lupus nephritis (LN) and high avidity of IgG ANAs (HA IgG ANAs) (p < 0.05). Furthermore, CXCL1 serum concentrations were significantly correlated with the SLE Disease Activity Index(SLEDAI) score, relative avidity index (RAI) of HA IgG ANAs and the levels of anti-dsDNA IgG, CRP, ESR, albumin, C3 and C4.Additionally, Statistical analysis revealed that positivity for IgG ANA (p < 0.001), the presence of HA IgG ANAs (p = 0.001) and the logarithmic level of anti-dsDNA IgG (p = 0.021) were significantly associated with the logarithmic level of CXCL1 with standard partial regression coefficients (95% CI) of 2.371 (1.734–3.009), 1.231 (0.52–1.937) and 0.409 (0.062–0.755), respectively. Finally, using cutoff points of 1182.17 pg/mL and 1500.31 pg/mL, serum CXCL1 levels had a similar sensitivity of 76% and specificity of 100% and 75% for the diagnosis of active SLE and LN, respectively.

Conclusions

Serum CXCL13 concentrations might represent a potential marker of disease activity in systemic lupus erythematosus.

The CXCL13 chemokine serves as a potential biomarker to diagnose systemic lupus erythematosus with disease activity

The aim of our study was to assess the regulatory response of the chemokine CXCL13 in the serum of systemic lupus erythematosus (SLE) patients with disease activity and to evaluate its influence on the inflammatory process in SLE. Serum samples from 97 SLE patients, 49 non-SLE patients (23 patients with other autoimmune diseases and 26 patients with rheumatoid arthritis) and 50 healthy controls were analyzed for the concentration of CXCL13 using ELISA. The results indicated that the serum levels of CXCL13 were significantly higher in SLE patients than in non-SLE patients and healthy controls (p < 0.001). Moreover, the level of CXCL13 decreased as the level of anti-dsDNA IgG decreased after treatment between the anti-dsDNA-positive SLE patients and the anti-dsDNA-negative SLE patients. In addition, serum CXCL13 levels were correlated with SLEDAI in different activities of SLE, renal involvement and active LN. Furthermore, the level of CXCL13 was positively related to the SLEDAI, level of anti-dsDNA IgG, level of ESR and RAI of high-avidity IgG ANAs (HA IgG ANAs). Additionally, statically analysis revealed that CXCL13 would be a best diagnostic value for determining the disease activity of SLE due to its moderate sensitivity (93.5%), specificity (95%), PPV (98.6%), NPV (79.2%) and OR(95%CI,250(30.303-1000)), at a cut-off level of 15.27 pg/mL. First, we indicated that CXCL13 was elevated in SLE patients regardless of the presence or absence of anti-dsDNA IgG ANAs. Furthermore, HA IgG ANAs might affect the circulation of CXCL13. Therefore, the chemokine CXCL13 might be a risk factor influencing the inflammatory process in SLE.

The major autoantibody epitope on factor H in atypical hemolytic uremic syndrome is structurally different from its homologous site in factor H-related protein 1, supporting a novel model for induction of autoimmunity in this disease

Atypical hemolytic uremic syndrome (aHUS) is characterized by complement attack against host cells due to mutations in complement proteins or autoantibodies against complement factor H (CFH). It is unknown why nearly all patients with autoimmune aHUS lack CFHR1 (CFH-related protein-1). These patients have autoantibodies against CFH domains 19 and 20 (CFH_19–20), which are nearly identical to CFHR1 domains 4 and 5 (CFHR1_4–5). Here, binding site mapping of autoantibodies from 17 patients using mutant CFH_19–20 constructs revealed an autoantibody epitope cluster within a loop on domain 20, next to the two buried residues that are different in CFH_19–20 and CFHR1_4–5. The crystal structure of CFHR1_4–5 revealed a difference in conformation of the autoantigenic loop in the C-terminal domains of CFH and CFHR1, explaining the variation in binding of autoantibodies from some aHUS patients to CFH_19–20 and CFHR1_4–5. The autoantigenic loop on CFH seems to be generally flexible, as its conformation in previously published structures of CFH_19–20 bound to the microbial protein OspE and a sialic acid glycan is somewhat altered. Cumulatively, our data suggest that association of CFHR1 deficiency with autoimmune aHUS could be due to the structural difference between CFHR1 and the autoantigenic CFH epitope, suggesting a novel explanation for CFHR1 deficiency in the pathogenesis of autoimmune aHUS.

Anti-chromatin and anti-histone antibodies in Egyptian patients with systemic lupus erythematosus

There has been a renewed interest in anti-chromatin and anti-histone antibodies in the last few years. To assess the prevalence of anti-chromatin and anti-histone antibodies in patients with systematic lupus erythematosus (SLE) and to correlate serum levels of these antibodies with clinical features of the disease, the presence of anti-chromatin and anti-histone antibodies in 38 patients with SLE was investigated by an enzyme-linked immunosorbent assay (ELISA). To determine the specificity of these antibodies, 15 patients with rheumatoid arthritis, 15 patients with systemic sclerosis, and 15 normal controls were also tested. Sensitivity of anti-chromatin antibodies in SLE patients was 89.5% and specificity was 80.0%, while sensitivity of anti-histone antibodies was 92.1% and specificity was 82.2%. Significant associations were found between the levels of anti-chromatin antibodies and arthritis, malar rash, oral ulcer, pulmonary affection (P < 0.05) also, lupus nephritis (P < 0.01), and disease activity score as measured by SLE disease activity index (SLEDAI; P < 0.001). Significant association was found between anti-histone antibodies and fatigue (P < 0.05). The incidence of positive anti-chromatin and anti-histone antibodies was significantly higher than that of anti-dsDNA antibodies in early stage of the disease. We conclude that anti-chromatin and anti-histone antibodies are both sensitive and specific for SLE and could be a useful addition to the laboratory tests that can help in the diagnosis of SLE. Anti-chromatin antibodies seem to be a promising marker useful in early diagnosis and assessment of disease activity in SLE patients especially in patients who are negative for anti-dsDNA antibodies.

The antichromatin antibodies can be useful as a diagnostic tool and disease activity marker of systemic lupus erythematosus in Koreans

We have investigated the clinical utility of antichromatin antibodies for the diagnosis of SLE and as a marker of disease activity in Korean SLE patients. Blood samples were collected from SLE patients, lupus syndrome patients having only two or three of ACR classification criteria for SLE and normal controls. The level of antichromatin antibody was measured by enzyme linked immunosorbent assay and expressed as arbitrary unit. The antichromatin antibody levels of the SLE and lupus syndrome patients were higher than NC. The antichromatin antibody levels were significant higher in SLE patients with arthritis. A significant correlation was found between the level of antichromatin antibodies and each of anti-dsDNA antibody, leukopenia, complement and SLEDAI. The change of antichromatin antibody levels showed a positive correlation with the change of SLEDAI in serial samples. These data suggest that the antichromatin antibodies appear to be a useful laboratory test that can help in the diagnosis and assessment of SLE.

Cis-Golgi matrix proteins move directly to endoplasmic reticulum exit sites by association with tubules

The role of cis-medial Golgi matrix proteins in retrograde traffic is poorly understood. We have used imaging techniques to understand the relationship between the cis-medial Golgi matrix and transmembrane proteins during retrograde traffic in control and brefeldin A (BFA)-treated cells. All five of the cis-medial matrix proteins tested were associated with retrograde tubules within 2-3 min of initiation of tubule formation. Then, at later time points (3-10 min), transmembrane proteins are apparent in the same tubules. Strikingly, both the matrix proteins and the transmembrane proteins moved directly to endoplasmic reticulum (ER) exit sites labeled with p58 and Sec13, and there seemed to be a specific interaction between the ER exit sites and the tips or branch points of the tubules enriched for the matrix proteins. After the initial interaction, Golgi matrix proteins accumulated rapidly (5-10 min) at ER exit sites, and Golgi transmembrane proteins accumulated at the same sites approximately 2 h later. Our data suggest that Golgi cis-medial matrix proteins participate in Golgi-to-ER traffic and play a novel role in tubule formation and targeting.

Fator antinúcleo na dermatologia

Trata-se de artigo de revisão e atualização sobre a pesquisa dos anticorpos antinucleares, em especial do fator antinúcleo, em que são abordados os aspectos históricos, epidemiológicos, fisiopatogenia, métodos de identificação, suas especificidades e interpretação, correlacionando-os com sua aplicabilidade na prática clínica do dermatologista e do clínico geral.

Concomitant early appearance of anti-ribonucleoprotein and anti-nucleosome antibodies in lupus prone mice

OBJECTIVE

To gain insights on initial stages of the autoimmune response in lupus prone mice taking advantage of new sensitive and quantitative techniques for the detection of autoantibodies specific for RNA- (ribonucleoproteins) and DNA-protein (chromatin) complexes.

METHODS

DNA and nucleosome antibodies were detected by ELISA, antibodies to SmB, U1A-RNP, Ro52, Ro60 and La by a new radioligand assay, using de novo synthesized radio-labeled antigens.

RESULTS

Analysis of anti-chromatin (including anti-nucleosome, anti-dsDNA and anti-histone antibodies) and of anti-snRNP antibodies (including anti-U1A-RNP, anti-SmB, anti-Ro52, anti-Ro60, anti-La antibodies) was performed in sequential sera from B/W, MRL+/+, MRL Yaa and MRL lpr/lpr mice. In a cohort of 105 MRL+/+ mice of different ages, 59, 51, and 57 mice were positive for anti-nucleosome, anti-SmB and anti-U1A-RNP, respectively. None of them was positive for anti-dsDNA. Importantly, antibody positivities were not randomly distributed but were significantly clustered in individual mice. Appearance of DNA- and RNA-protein complex antibodies started at approximately 18-20 weeks of age, preceding that of the anti-dsDNA (or anti-histone) antibodies that only started at 30-32 weeks. Anti-nucleosome, anti-SmB and anti-U1A-RNP antibody responses did not display any cross-reactivity as demonstrated by inhibition and adsorption experiments.

CONCLUSION

These data indicate that anti-nucleosome and anti-snRNP antibodies appear early and concomitantly in lupus prone mice even though they do not share any cross-reactivity. These results fit with the assumption that their production is triggered by tightly physically associated nucleosomes and snRNP autoantigens contained in the same apoptotic bodies.

Autoantibodies in childhood post-varicella acute cerebellar ataxia

BACKGROUND

Anti-Purkinje cell antibodies have been reported in cerebellar ataxia following Epstein-Barr virus (EBV) infection. We investigated autoantibody responses, including anti-Purkinje cell antibodies, and the clinical course in eight children who developed post-varicella ataxia, five of their siblings with uncomplicated varicella, one child with post-EBV ataxia, two children with acute disseminated encephalomyelitis (ADEM) and one with neuroblastoma associated ataxia, and in age and gender matched controls.

METHODS

Autoantibodies were tested by indirect immunofluorescence (IIF) on cryopreserved cerebrum and cerebellum sections. Other autoantibodies were measured by conventional IIF protocols using HEp-2 cells as a substrate. Antibodies to myelin associated glycoprotein (MAG), asialo-GM1, beta2 glycoprotein 1, cardiolipin and myelin basic protein (MBP) were measured by ELISA.

RESULTS

Three of eight children with acute post-varicella ataxia, one child with post-EBV ataxia, one child with ADEM and one child with uncomplicated varicella, had high titer autoantibodies (>1/160) that reacted with cerebrum and cerebellar tissue. This reactivity was not seen in one child with ADEM, in one with neuroblastoma and ataxia, in the remainder of the children with uncomplicated varicella or age and gender matched controls. Autoantibodies were not seen in CSF from two children with post-varicella ataxia. The punctate staining seen on cerebrum and cerebellum sections co-localized with rabbit antibodies to the centrosome protein pericentrin. All patients with strong reactivity with cerebrum and cerebellar tissue by IIF had elevated levels of anti-MAG that was not confirmed by absorption assay. No reactivity was seen with asialo-GM1, MBP, beta2 glycoprotein 1 or cardiolipin. None of the sera had autoantibodies directed against endosomes, the Golgi complex, or the paraneoplastic autoantigens Hu and Yo.

CONCLUSION

Some children with post-viral ataxia develop antibodies that have strong reactivity with cerebral and cerebellar tissue. Some of the antigenic reactivity co-localized with the centrosome protein pericentrin.

Presence of antinucleosome autoantibodies in a restricted set of connective tissue diseases: antinucleosome antibodies of the IgG3 subclass are markers of renal pathogenicity in systemic lupus erythematosus

OBJECTIVE

To study the frequency and disease specificity of antinucleosome antibody reactivity in diverse connective tissue diseases (CTD), and to determine factors, such as antibody subclass, that may influence the pathogenicity of these antibodies in relation to disease activity.

METHODS

IgG and IgM antinucleosome activities on nucleosome core particles from 496 patients with 13 different CTD and 100 patients with hepatitis C were measured by enzyme-linked immunosorbent assay (ELISA). Of the patients with CTD, 120 had systemic lupus erythematosus (SLE), 37 had scleroderma (systemic sclerosis; SSc), 20 had mixed connective tissue disease (MCTD), and 319 had other CTD, including Sjögren's syndrome, inflammatory myopathy, rheumatoid arthritis, primary antiphospholipid syndrome, Wegener's granulomatosis, Takayasu arteritis, giant cell arteritis, relapsing polychondritis, Behçet's syndrome, and sarcoidosis. Antinucleosome-positive sera were further analyzed, by isotype-specific ELISA, for antinucleosome and anti-double-stranded DNA (anti-dsDNA) IgG subclasses.

RESULTS

SLE, SSc, and MCTD were the only 3 CTD in which antinucleosome IgG were detected (71.7%, 45.9%, and 45.0% of patients, respectively). Antinucleosomes of the IgG3 subclass were present at high levels in patients with active SLE and were virtually absent in those with SSc, MCTD, or inactive SLE, and their levels showed a positive correlation with SLE disease activity. Of note, an increase in levels of antinucleosome of the IgG3 isotype was observed during SLE flares, and this increase was found to be closely associated with active nephritis. Levels of antinucleosome of the IgG1 subclass showed a trend toward an inverse correlation with SLE disease activity. No significant fluctuation in the anti-dsDNA isotype profile was observed in relation to SLE severity or clinical signs.

CONCLUSION

Our data suggest that IgG antinucleosome is a new marker that may help in the differential diagnosis of CTD; antinucleosome of the IgG3 isotype might constitute a selective biologic marker of active SLE, in particular, of lupus nephritis.

Antibodies to fibrin-bound tissue-type plasminogen activator in systemic lupus erythematosus are associated with Raynaud's phenomenon and thrombosis

Fibrinolysis triggered by t-PA bound to fibrin is one of the main antithrombotic mechanisms. Defects in the fibrinolytic system-decreased tissue-type plasminogen activator (t-PA) activity and elevated levels of plasminogen activator inhibitor (PAI-1), in patients with SLE have been associated with an increased tendency to thrombosis. In the present study, 43 patients with SLE fulfilling the ACR criteria for the disease, were studied for the presence of autoantibodies to fibrin-bound t-PA, i.e. the physiological active form of this plasminogen activator. A solution of 200 IU/ml of t-PA was incubated with solid-phase fibrin prepared as previously described (Anal Biochem 1986; 153; 201-210). Sera diluted 1:50 were incubated with fibrin-bound t-PA, the plates were then washed, and bound immunoglobulins were detected using a polyvalent peroxidase-labeled goat anti-human Ig. Plates coated with fibrin alone were used as controls. Sera were considered positive when A490/630 obtained with normal human sera in two independent test was greater than the mean plus 2 SD. Eleven of 43 (26%) SLE sera demonstrated antibody reactivity against fibrin-bound t-PA. Within the anti-t-PA positive group there was a higher proportion of SLE patients with severe Raynaud's phenomenon and thrombotic events when compared to the anti-t-PA negative group: 36% vs 6% and 18% vs 6% respectively. These results suggest that autoantibodies to fibrin-bound t-PA could play a role in the pathogenesis of vascular disease in some SLE patients.

Evaluation of recombinant Ro/SSA, La/SSB, Sm, and U1 RNP autoantigens in clinical diagnosis

This study comprises an analysis of the diagnostic usefulness of Ro/SSA, La/SSB, Sm and U1 RNP autoantigens obtained by DNA recombinant technology. We studied the presence of these autoantibodies in 33 patients with systemic lupus erythematosus (SLE) and 30 normal individuals by enzyme-linked immunosorbent assay (ELISA) using recombinant autoantigens and by Western immunoblot with these same antigens obtained from natural sources (rabbit thymus and human spleen). The strength of agreement between results found with these two techniques was moderate in the case of anti-Ro/SSA (kappa = 0.474, P < 0.001) and anti-U1 RNP (kappa = 0.566. P < 0.001) antibodies and almost perfect in the case of anti-La/SSB (kappa = 0871, P < 0.001) and anti-Sm (kappa = 0.833, P < 0.001). Furthermore, analysis of the disagreement between the two techniques evidenced a measurement bias for anti-Ro/SSA and anti-U1 RNP antibodies (Mc NEMAR'S statistic 13 and 11, respectively) whose direction, though difficult to define in the absence of a gold standard for such determinations, could be accounted for by the ELISA technique's greater tendency to produce positive results. Our conclusion is that the diagnostic usefulness of recombinant La/SSB and Sm autoantigens has been satisfactorily proven, whereas the case of the Ro/SSA and U1 RNP systems should be subject to further in-depth study of the autoepitopes recognised and the possible modifications which the latter might undergo as a result of their obtension from procariotic sources.

A rapid and semi-quantitative method for the detection of autoantibodies by multiple spot immunoassay

A method for rapid simultaneous determination of multiple autoantibodies in sera has been developed. 42 different antigens were coated onto a nitrocellulose membrane in a miniblotter apparatus with 42 lanes. The membrane was also coated with different concentrations of human IgG to create a standard curve. The blotting apparatus after coating, blocking and washing was turned 90 degrees so that all lanes crossed the antigen coated lanes. Thereafter, 42 sera were incubated with the antigens. After this stage the membrane was treated as in the usual dot-blot procedure. After incubation with alkaline phosphatase labelled anti-human IgG, staining and drying of the membrane, the staining intensity of individual lanes was scanned into a data file and analyzed by computer. By this method it was possible in 4 h to examine 42 sera for autoantibodies against 42 antigens, i.e., more than 1600 tests. Furthermore, the amount of antibody could be semi-quantified, using the IgG standards. The method should be useful for rapid screening of autoantibodies in a routine laboratory.

Isolation and characterization of a cartilage-specific membrane antigen (CH65): comparison with cytokeratins and heat-shock proteins

We report the isolation and characterization of a 65,000 MW chondrocyte autoantigen (CH65) which may be involved in rheumatoid arthritis. This chondrocyte-specific antigen reacted with sera from patients with rheumatoid arthritis (RA). CH65 did not cross-react with a polyclonal antibody raised against microbial heat-shock protein (hsp) 65, anti-human hsp 65 monoclonal antibodies (mAb) (LK1 and LK2), anti-microbial hsp 65 mAb (IA10, IIC8 and WTB-78H1) and anti-cytokeratin 8, 18, 19 mAb (NCL5D3MAb). CH65 could be purified from chicken chondrocyte membranes by ammonium sulphate precipitation and a novel electro-gel-filtration method. The amino acid analysis yielded an unusually high degree of glycine, serine and asparagine residues. The internal amino acid sequence obtained by tryptic digestion revealed homologies with the cytokeratin family. Despite these homologies, CH65 lacked immunological cross-reactivity with commercial anti-cytokeratin antibodies. Mice mAb generated against the purified CH65 (C6) were used to identify the protein as a tissue-specific constitutive protein membrane from chondrocytes. Sera from patients with RA cross-reacted with purified CH65. The stress or heat-shock protein (hsp 65), implicated in the development of experimental and clinical arthritis, showed no immunological cross-reactivity with CH65 in Western blots. These findings suggest that CH65 may represent an interesting cartilage-specific new antigen in RA. The availability of this antigen in purified form and specific mAb may offer useful tools in arthritis research.

Sera from patients with rheumatic diseases recognize different epitope regions on the 52-kD Ro/SS-A protein

Patients suffering from systemic lupus erythematosus (SLE) or Sjögren's syndrome (SS) often contain autoantibodies directed to the Ro(SS-A) complex. In this study the antigenic determinants on two of the components of the Ro complex, i.e. the Ro60 and the Ro52 polypeptides, were investigated. Anti-Ro+ sera were selected by counter-immunoelectrophoresis. Depending on the detection method, 59-68% of the SLE patients produced anti-Ro but not anti-La antibody, while 72-81% of the SS patients produced both anti-Ro and anti-La antibody. Immunoprecipitation of recombinant Ro-proteins showed that 61 sera (87%) were reactive with both Ro proteins, seven sera with Ro60 only, one serum with Ro52 only, and one serum did not precipitate the proteins at all. The anti-Ro60 reactivity of human sera is strongly associated with the native form of Ro60, suggesting that conformational autoepitopes are an important feature of Ro60. In the case of Ro52, frequently the residues located between amino acids 216 and 292 were essential for reactivity with the antibodies. With 70% of the lupus sera tested this appeared to be the only region important for reactivity. The antibodies of SS patients generally recognized multiple B cell epitopes located between amino acids 55 and 292. The results of this study indicate that the antigenic determinants on Ro52 are different for autoantibodies produced by lupus patients compared with those of SS patients.

Molecular characterization of two human autoantigens: unique cDNAs encoding 95- and 160-kD proteins of a putative family in the Golgi complex

Serum autoantibodies from a patient with autoantibodies directed against the Golgi complex were used to screen clones from a HepG2 lambda Zap cDNA library. Three related clones, designated SY2, SY10, and SY11, encoding two distinct polypeptides were purified for further analysis. Antibodies affinity purified by adsorption to the lambda Zap-cloned recombinant proteins and antibodies from NZW rabbits immunized with purified recombinant proteins reproduced Golgi staining and bound two different proteins, 95 and 160 kD, from whole cell extracts. The SY11 protein was provisionally named golgin-95 and the SY2/SY10 protein was named golgin-160. The deduced amino acid sequence of the cDNA clone of SY2 and SY11 represented 58.7- and 70-kD proteins of 568 and 620 amino acids. The in vitro translation products of SY2 and SY11 cDNAs migrated in SDS-PAGE at 65 and 95 kD, respectively. The in vitro translated proteins were immunoprecipitated by human anti-Golgi serum or immune rabbit serum, but not by normal human serum or preimmune rabbit serum. Features of the cDNA suggested that SY11 was a full-length clone encoding golgin-95 but SY2 and SY10 together encoded a partial sequence of golgin-160. Analysis of the SY11 recombinant protein identified a leucine zipper spanning positions 419-455, a glutamic acid-rich tract spanning positions 322-333, and a proline-rich tract spanning positions 67-73. A search of the SwissProt data bank indicated sequence similarity of SY11 to human restin, the heavy chain of kinesin, and the heavy chain of myosin. SY2 shared sequence similarity with the heavy chain of myosin, the USO1 transport protein from yeast, and the 150-kD cytoplasmic dynein-associated polypeptide. Sequence analysis demonstrated that golgin-95 and golgin-160 share 43% sequence similarity and, therefore, may be functionally related proteins.

Epitope mapping of histone 5 (H5) with systemic lupus erythematosus, procainamide-induced lupus and hydralazine-induced lupus sera

To define the linear epitopes on H5 that react with systemic lupus erythematosus (SLE) and drug-induced lupus (DIL) sera, concurrent overlapping hexameric peptides corresponding to the sequence of H5 were synthesized by stepwise elongation of the polypeptide chains on polyethylene supports. The hexapeptides were tested for reactivity with 8 SLE and 8 DIL sera using an enzyme linked immunosorbent assay (ELISA). SLE and hydralazine-induced lupus (HIL) antibodies were most reactive with peptide 45 (SSRQSI) and patients with procainamide-induced lupus (PIL) were most reactive with peptide 24 (SHPTYS). The epitopes of highest reactivity were in the globular domain of H5. Low reactivity was observed with carboxyl terminal peptides. These findings differ from immunoblotting studies of protease cleaved peptides which have previously shown that the H5 determinants are in the carboxyl terminus.

Autoantibodies in scleroderma

Autoantibodies directed against nuclear, nucleolar, and a number of cytoplasmic components are described in the sera of scleroderma patients. Early studies of autoantibodies that relied on cryopreserved sections of rodent organ substrates showed that approximately 50% of scleroderma patients had anti-nuclear antibodies (ANA). More recent studies that have used tissue culture cell substrates have shown that up to 98% of scleroderma patients have a positive ANA. In all of these studies, the presence of different patterns of staining have suggested that scleroderma sera reacted with a variety of intracellular antigens. The use of molecular and immunochemical techniques has now shown that over 20 intracellular autoantigens are targets of autoantibodies in scleroderma sera. Clinical studies have shown that these autoantibodies are important diagnostic and prognostic markers in scleroderma. In the future, autoantibody testing may be used to monitor the patient's response to immunological therapies.